1. Field of the Invention
The present invention relates to a medical diagnostic signal detection apparatus and a medical diagnostic signal detection method, and particularly relates to a signal detection apparatus which receives a multichannel signal and a signal detection method therefor.
2. Background Art
In a medical diagnostic apparatus such as an ultrasonic diagnostic apparatus or a sonar, multichannel signals are required to be received in order to obtain a highly accurate image. The total power loss of all channels increases due to the use of multichannel reception circuits. In addition, in a case where multichannel transmission circuits are also necessary as in the ultrasonic diagnostic apparatus, the power loss is also considerable during operations thereof. Therefore, a heat generation problem due to the power loss may be more serious than before. In other words, a temperature fluctuation occurs in a module or an IC chip due to the heat generation, and a power supply voltage fluctuation also occurs as a result of the temperature fluctuation.
A threshold voltage or mobility of a MOS transistor forming a circuit of each channel fluctuates due to the temperature fluctuation. A sa result of the fluctuation and the power supply voltage fluctuation, a gain, a DC offset voltage, and a frequency bandwidth of an amplifier or an analog-digital converter fluctuate. In addition, a delay time of a clock buffer which supplies a sampling clock to the analog-digital converter also fluctuates, and thus sampling timing of the analog-digital converter also fluctuates.
Since a temperature or a power supply voltage cannot be expected to be uniform in all of the channels, a mismatch in the temperature or the power supply voltage between the channels causes mismatches in gain, DC offset voltage, frequency bandwidth, and sampling timing between the channels. As a result, an artifact (false image) is generated in a final image, and thus the accuracy of a medical diagnostic apparatus or a sonar is reduced.
In JP-A-4-114637, in a system including a plurality of channels, a common reference voltage is supplied to the channels during testing of a correction value, and an output value of each channel is acquired. Next, a correction value for correcting a gain mismatch between amplifiers of the respective channels is obtained on the basis of the result.
During reception, a gain of the amplifier of each channel is adjusted by using the correction value obtained during the correction value test as described above, and thus the gain mismatch between the amplifiers is removed. However, in this method, while each channel performs reception, a reference voltage for correction cannot be supplied to the channels, and thus a correction value cannot be tested.